I have an old but working Rauland-Borg ("Webster") SS amp that I'd like to use as a subwoofer amp driving a 2x15 4 ohm cab. The amp has 70V and 25V output options. I believe the correct formula to arrive at output impedance is Output Voltage squared divided by nameplate output watts = speaker ohms.
So in my case, 25 squared divided by 125 = 5 ohms.
My cabinet is 4 ohms and I know I could open it up and put the 2- 15's in series (16 ohms) but should I "cheat" and leave the cab at 4 ohms? Or, is there another workaround other than to go the series route?
Thanks.
So in my case, 25 squared divided by 125 = 5 ohms.
My cabinet is 4 ohms and I know I could open it up and put the 2- 15's in series (16 ohms) but should I "cheat" and leave the cab at 4 ohms? Or, is there another workaround other than to go the series route?
Thanks.
Thanks. The only output configuration available is for 70 or 25v hence I applied the formula to arrive at 5 ohms. My concern is that I don't want to damage the amp by connecting to a 4 ohm load. I don't know what the amp tolerance might be since according to the formula the amp wants to see a minimum 5 ohm load.
You will need a 70volt line transformer at the power the amplifier will supply. If it delivers 125Watts into any given load, you need a transformer rated 70volt line at 125Watts.
This is a public address amplifier for use with horn type loudspeakers that have an integral tapped transformer.
See link; http://www.pas-sound.co.uk/Basic 100v system wiring guide .pdf
This is a public address amplifier for use with horn type loudspeakers that have an integral tapped transformer.
See link; http://www.pas-sound.co.uk/Basic 100v system wiring guide .pdf
Thanks. The amp worked fine when I connected to a 2x12 16R cabinet I had so I don't think I need a 125Watt/70V transformer to use with a X ohm speaker. I am hoping someone knows whether I need to reconfigure the 2x15 cabinet to create a 16R load or whether the existing 4R configuration will harm the amp that theoretically wants a minimum 5R load. I've attached a partial schematic of a similar Rauland-Borg amp.
Attachments
Please do yourself a favor and look up "constant voltage" speaker systems, also called 70.7 volt systems. They do come in 25v and 100v flavors as well.
You can stick your load on the 25v winding and probably get away with it, but have you tried it with a real thumping passage? Your schematic shows 50 ohms across the 70v output and 6 across the 25, but those outputs are intended to drive transformers.
Your schematic calls it a 100 watt amp.
You can stick your load on the 25v winding and probably get away with it, but have you tried it with a real thumping passage? Your schematic shows 50 ohms across the 70v output and 6 across the 25, but those outputs are intended to drive transformers.
Your schematic calls it a 100 watt amp.
These will drive speakers directly. I had a bunch of them. Massive beasts for their power. The ratings are somewhat conservative.
But 25V is 78 Watts in 8 Ohms, so 156 Watts in 4 Ohms. This is 25% above the nominal wattage. In "nice" work, seldom clipped, I'm quite sure they will be fine. As a stage amp, where clipping may be frequent, they may fail in time.
I recall their clipping as "not rude" but "not nice".
There is _NO_ protection on the output devices. The undersize main cap and transformer losses prevent "infinite" current like a hi-fi amp, and the breaker will pop if you keep it up, but in stage-work I am sure you can kill it.
These days, 125W-156W is not much of a bass amp, and 200++Watt bass amps are readily available at prices less than parts+labor to fix a blown-up Rauland. Also lighter by avoiding the OPT.
But 25V is 78 Watts in 8 Ohms, so 156 Watts in 4 Ohms. This is 25% above the nominal wattage. In "nice" work, seldom clipped, I'm quite sure they will be fine. As a stage amp, where clipping may be frequent, they may fail in time.
I recall their clipping as "not rude" but "not nice".
There is _NO_ protection on the output devices. The undersize main cap and transformer losses prevent "infinite" current like a hi-fi amp, and the breaker will pop if you keep it up, but in stage-work I am sure you can kill it.
These days, 125W-156W is not much of a bass amp, and 200++Watt bass amps are readily available at prices less than parts+labor to fix a blown-up Rauland. Also lighter by avoiding the OPT.
Thanks Enzo. I don't know much about CV systems except that they are primarily intended to be used to drive multiple speakers over large distances like paging speakers in a shopping mall. My amp was originally part of a system of speakers in a cafeteria. The schematic I attached is for 100W amp but is the closest I could find to mine which is labelled 125W. I haven't really paid attention to the response during a "real thumping passage". What should I listen for? Am I going to destroy this amp if driving into a 4 ohm load?
Thanks. I guess I don't have a lot to lose! I host regular "jams" at my home and just want to give a little boost to the bass guitar and kick coming out of an active crossover.
If you are going to load your amp directly with the speakers anyway at least rewire them for the 16 ohm load.
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